Combined solvent assisted

Choosing a Mobile Phase Several indices have been developed to assist in selecting a mobile phase, the most useful of which is the polarity index. Table 12.3 provides values for the polarity index, P, of several commonly used mobile phases, in which larger values of P correspond to more polar solvents. Mobile phases of intermediate polarity can be fashioned by mixing together two or more of the mobile phases in Table 12.3. For example, a binary mobile phase made by combining solvents A and B has a polarity index, of... 

The relations 4- > 2-position in rate and 4- < 2-position in will apparently apply to reactions with anions, but the reverse relation is observed in piperidination, presumably due to 2-substitution being favored by hydrogen bonding in the zwitterionic transition state (cf. 47, 59, and 277) or by solvent-assisted proton removal from the intermediate complex (235). Substitutions of polychloroquino-lines (in which there is a combined effect of azine-nitrogen and unequal mutual activation of the chlorine substituents) also show 4- > 2-position in reactivity contrary statements are documented by these same references. Examples are cited below of the relation 2- > 4-position when a protonated substrate or a cyclic transition state is involved. 

In order to accelerate sample preparation, new extraction methodologies such as accelerated solvent extraction (ASE) and MAE, based on the use of elevated temperature and pressure to heat the mixture sample-solvent, have been recently developed and applied for PAH extraction from meat [695] and vegetables [696-698]. Garda Falcon et al. [699] used microwave treatment with hexane to accelerate PAH extraction from freeze-dried foods. The fat extracted in this way underwent microwave assisted saponification with ethanolic KOH. Hernandez-Borges et al. [700] combined microwave-assisted hydrolysis and extraction to isolate organic pollutants from mussels, while... 

It is very common to combine methods in obtaining aroma isolates. The simultaneous distillation/extraction method previously described is an example. Another popular combination method initially involves the solvent extraction of volatiles from a food and then high-vacuum distillation of the solvent/aroma extract to provide a fat-free aroma isolate. This technique is broadly used today to provide high-quality aroma extracts for numerous purposes. The apparatus used in solvent removal has been improved upon to reduce analysis time and efficiency the modified method is termed solvent-assisted flavour extraction (SAFE) [16]. 

In contrast, solvent-assisted molding uses an elastomeric polydimethylsiloxane (PDM S) mold in combination with an appropriate solvent instead of a rigid mold and high temperature/pressure to emboss the polymer film. The solvent, rather than temperature, softens the polymer. Solvent is either briefly applied to the PDMS mold [9] or retained in the polymer film [18] before placing the two surfaces in contact. The polymer is drawn into the cavities of the mold as solvent is removed from the mold-polymer interface by transport and evaporation. The permeable mold prevents trapping of air pockets and non-uniform solvent evaporation. After evaporation of the solvent, the mold is removed, leaving behind a relief structure complementary to its topography. 

Solvent-assisted flavor evaporation (SAFE)—a new and versatile technique for the careful and direct isolation of aroma compounds from complex food matrices—was developed in 1999 by W. Engel et al. (104). Technical details and the design of the SAFE apparatus are exhaustively described by the authors. SAFE includes a compact distillation unit in combination with a high vacuum pump (Fig. 20). The developers of this new equipment pointed out the following advantages ... 

The development of the novel Davy-McKee combined mixer—settler (CMS) has been described (121). It consists of a single vessel (Fig. 13d) in which three 2ones coexist under operating conditions. A detailed description of units used for uranium recovery has been reported (122), and the units have also been studied at the laboratory scale (123). AppHcation of the Davy combined mixer electrostatically assisted settler (CMAS) to copper stripping from an organic solvent extraction solution has been reported (124). 

A 250-ml three-necked flask is fitted with a condenser (drying tube). The system is flushed with dry nitrogen, and a dry nitrogen atmosphere is maintained. In the flask is placed a solution of potassium /-butoxide (2.8 g, 0.025 mole) in dry /-butyl alcohol (100 ml). 4-Benzoyloxycyclohexanone (5 g, 0.022 mole, Chapter 7, Section X) is added to the solution, the transfer being assisted by the use of 10-15 ml of dry /-butyl alcohol. The mixture is cautiously brought to reflux, and refluxing is continued for 45 minutes. The mixture is then cooled rapidly to room temperature and carefully acidified by the addition of 10 ml of 6 A hydrochloric acid (potassium chloride will precipitate). The mixture is placed on a rotary evaporator and the bulk of the solvent is removed. The residue is diluted with sufficient water to dissolve the potassium chloride and extracted three times with 50-ml portions of ether. The ether extracts are combined and extracted four times with 100-ml portions of aqueous 5% sodium bicarbonate solution. The bicarbonate extracts are combined and the solution is acidified by the addition of concentrated hydrochloric acid to pH 4. The mixture is now extracted three times with 100-ml portions of ether, the combined ethereal extracts are washed with water, then dried, and the solvent is removed. The residual product may be recrystallized from benzene-hexane. The acid has mp 65-68°. 

Microwave-assisted Diels-Alder reactions have been performed in solvents [38, 39], in free solvent conditions [38c, 40], in solid phase [39, 41] and in the presence of Lewis acids [38c]. Sometimes some of these reaction conditions were combined. 

The Suzuki reaction has been successfully used to introduce new C - C bonds into 2-pyridones [75,83,84]. The use of microwave irradiation in transition-metal-catalyzed transformations is reported to decrease reaction times [52]. Still, there is, to our knowledge, only one example where a microwave-assisted Suzuki reaction has been performed on a quinolin-2(lH)-one or any other 2-pyridone containing heterocycle. Glasnov et al. described a Suzuki reaction of 4-chloro-quinolin-2(lff)-one with phenylboronic acid in presence of a palladium-catalyst under microwave irradiation (Scheme 13) [53]. After screening different conditions to improve the conversion and isolated yield of the desired aryl substituted quinolin-2( lff)-one 47, they found that a combination of palladium acetate and triphenylphosphine as catalyst (0.5 mol %), a 3 1 mixture of 1,2-dimethoxyethane (DME) and water as solvent, triethyl-amine as base, and irradiation for 30 min at 150 °C gave the best result. Crucial for the reaction was the temperature and the amount of water in the... 

LC-APCI-MS is a derivative of discharge-assisted thermospray, where the eluent is ionised at atmospheric pressure. In an atmospheric pressure chemical ionisation (APCI) interface, the column effluent is nebulised, e.g. by pneumatic or thermospray nebulisation, into a heated tube, which vaporises nearly all of the solvent. The solvent vapour acts as a reagent gas and enters the APCI source, where ions are generated with the help of electrons from a corona discharge source. The analytes are ionised by common gas-phase ion-molecule reactions, such as proton transfer. This is the second-most common LC-MS interface in use today (despite its recent introduction) and most manufacturers offer a combined ESI/APCI source. LC-APCI-MS interfaces are easy to operate, robust and do not require extensive optimisation of experimental parameters. They can be used with a wide variety of solvent compositions, including pure aqueous solvents, and with liquid flow-rates up to 2mLmin-1. 

Domin, M. A. Welham, K. J. Ashton, D. S. The effect of solvent and matrix combinations on the analysis of bacteria by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Rapid Comm. Mass Spectrom. 1999,13,222-226. 

Solutions of Ru3(CO)i2 in carboxylic acids are active catalysts for hydrogenation of carbon monoxide at low pressures (below 340 atm). Methanol is the major product (obtained as its ester), and smaller amounts of ethylene glycol diester are also formed. At 340 atm and 260°C a combined rate to these products of 8.3 x 10 3 turnovers s-1 was observed in acetic acid solvent. Similar rates to methanol are obtainable in other polar solvents, but ethylene glycol is not observed under these conditions except in the presence of carboxylic acids. Studies of this reaction, including infrared measurements under reaction conditions, were carried out to determine the nature of the catalyst and the mechanism of glycol formation. A reaction scheme is proposed in which the function of the carboxylic acid is to assist in converting a coordinated formaldehyde intermediate into a glycol precursor. 

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